This is something I put a bit of thought into with my recent decision to get a modern Kindle. Chiefly it was driven by two facts about my old HDX7: it’s so old, I can’t remember what year the lock screen adds last refreshed never mind how many years “Yeah, that’s not supported anymore. Please use a browser instead.” has been the answer to various functions.
Secondly of course is the fact that my HDX was mostly used for reading, not for apps. Getting an e-Ink model was a natural choice versus another Fire series. For the most part, I think there’s only two things I could see that would make me upgrade before my Kindle is likewise old as heck.
1/ USB-C because the only other devices I typically charge that still use USB Micro-B are things like headphones and speakers. Devices that aren’t likely to retire until they break, no longer hold a suitable charge, or become a source of pain over the aging Bluetooth standards. So things that will probably die by the time USB connectors other than Type-C have gone the way of the floppy diskette.2/ Tremendous boost in US performance. Because tasks like looking up words or shifting through annotations ain’t very fast on the Kindle 10 by any means. But when you consider that it’s hard to make the device any cheaper, and the SoC has enough oomph not to worry about ebooks exceeding its capabilities: it’s hard to complain about showing some patience for infrequently used interfaces to finally open.
Let’s say I’m not expecting to buy a new Kindle in a very long time unless I run out of Micro USB charging cables, lol